This project continues the study of sperm transport in the female reproductive tract. Sperm transport is a sophisticated process whose control is exerted at the levels of both the sperm and the female reproductive tract. Although approximately 20 females have had daily monitoring of urinary steroid hormones, only three female cynos have been actually utilized on this project. This project requires that females be mated with a proven fertile male within one day prior to ovulation. Three cynomolgus monkeys have been studied at twenty four hours after a single timed mating in the periovulatory period. Mating was scheduled on the basis of the midcycle rise in urinary estrogen metabolites and was confirmed by a rapid serum estrogen assay. Mating was confirmed by post-coital evaluation of the cervical mucus. The reproductive tracts were perfused and fixed and serial sections of the entire oviducts were examined. Oviductal sperm were present in one of the three animals. The sperm were located in a discrete region of the oviductal isthmus immediately caudal to the ampullar-isthmic junction. This region may be the site of the tubal sperm reservoir.